British Prime Minister Theresa May said Monday she was looking forward to hosting US President Donald Trump in a state visit, after more than a million people signed a petition demanding the invitation be withdrawn following his controversial travel ban.

Already under pressure over her ties to Trump, May is also facing calls by members of her own Conservative party to reconsider the visit, which would see Trump honoured by parliament and Queen Elizabeth II.

May's Downing Street office said she does not agree with the US ban on refugees and citizens of seven mainly Muslim countries, but still refused to back down on the visit.

"The prime minister extended an invitation on behalf of the queen, and she was very happy to do so. The USA is one of this country's closest allies, and we look forward to hosting the president later this year," a spokesman said.

May announced the state visit during a meeting with Trump at the White House on Friday, which was intended to reaffirm the "special relationship" and boost trade ties after Britain leaves the European Union.

But her closeness to the erratic billionaire drew fire at home, particularly when she initially failed to condemn the travel ban, saying it was a US affair.

By Monday morning, more than one million people had signed an online petition calling for the state visit to be cancelled because his "well-documented misogyny and vulgarity disqualifies him" from meeting the queen.

Set up several months ago, the number of signatories has surged since Trump signed his contentious executive order on Friday -- a move that triggered global protests, with more expected in Britain later Monday.

"You are not welcome here, Mr President," the Daily Mirror tabloid said in a headline.

Tens of thousands joined the anti-Trump rally in London, a police source said

(AFP)

Opposition Labour leader Jeremy Corbyn, the smaller Liberal Democrats and the Scottish National Party have all called for the state visit to be cancelled, as have some from May's own party.

"We have to question whether... this is something that Britain should be doing for a man who has no respect for women, disdain for minorities, little value for LGBT communities, no compassion for the vulnerable and whose policies are rooted in divisive rhetoric," Sayeeda Warsi, a Muslim member of the upper House of Lords for the Conservatives, told BBC radio.

Ruth Davidson, leader of the Scottish Conservatives, said the visit should not go ahead "while a cruel and divisive policy which discriminates against citizens of the host nation is in place".

'Divisive and wrong'

Trump's order suspended the arrival of all refugees for at least 120 days, Syrian refugees indefinitely, and barred citizens from Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen for 90 days.

The British foreign minister Boris Johnson told parliament on Monday that it was "divisive and wrong to stigmatise because of nationality", confirming that, after talks with the US administration, most Britons would be exempt.

However, Johnson said there was "no reason" why Trump shouldn't receive a state visit, calling the US-UK relationship the "single most important geopolitical fact of the last 100 years."

High-profile British citizens briefly caught up in the new US rules included Somali-born Olympic champion Mo Farah, who slammed a policy based on "ignorance and prejudice" that could keep him apart from his US-based family.

The Foreign Office later announced the order would only apply to individuals travelling directly to the United States from one of the seven listed countries.

However, there was some confusion when the US embassy in London said that anyone with a passport from those countries would not get a visa there.

Trump, whose mother was born in Scotland, has made clear his fondness for Britain and has said last summer's Brexit vote was a "smart" move.